Automated bulk optical processing equipment can perform a variety of tasks such as, for example, inspecting or sorting bulk articles including raw or processed fruit, vegetables, wood chips, recycled plastics and other similar products. The articles may be characterized according to size, color, shape or other qualities. Modern bulk optical processing equipment can rapidly separate very large quantities of articles into numerous categories.
Such equipment typically includes a conveyor system that moves the articles past an inspection station where cameras or other detection devices examine the articles. The inspection station sends signals to a sorting or treatment station where the articles are sorted or otherwise treated by category. For example, defective or foreign articles may be removed from the flow of articles carried by the conveyor system.
Rapid inspection or sorting of large quantities of articles typically requires high-speed conveyor systems such as, for example, conveyor belts with widths of 3-4 ft (1-1.3 m) and that carry articles at speeds of over 10 ft/sec (3 m/sec). A problem with conveyor systems driven at such speeds is that many articles are relatively unstable on the belts and tend to roll, tumble, bounce and collide with each other. Unstable articles carried by a high-speed conveyor system are difficult to inspect, sort or otherwise process for at least two reasons.
First, automated bulk optical processing equipment includes cameras or other optical detectors that optically determine selected characteristics of the articles (e.g., size, color or shape). The rolling, tumbling or bouncing of an article typically diminishes the clarity with which an image of the article is generated, thereby decreasing the accuracy and reliability of the optical information about the article. As extreme examples, rolling could cause a cubic article to appear round or an article with regions of two different colors to be of a single mixed color.
Second, unstable articles moving on a conveyor belt can move laterally across the belt or along the belt in its direction of travel. Lateral movement of the articles is undesirable because it misaligns the articles as they pass from the inspection station to the processing station, thereby resulting in incorrect processing. Similarly, articles that move along the belt in its direction of travel have different effective speeds along the belt and may be temporally misaligned for subsequent processing operations.
Some articles have increased susceptibility to unstable motion on a conveyor, such as light-weight articles and articles of low and non-uniform density (e.g., wood and bark chips). As a consequence, these types of articles are correspondingly difficult to inspect and sort accurately at high speeds.
To decrease the instability of articles resulting in image degradation and processing errors, some conveyor systems operate at reduced speeds or have greater lengths. Such systems are undesirable because the reduced speeds result in lower processing rates and the conveyor systems of greater length can limit the placement of such systems.